Employing radar systems for detecting intrusions into protected areas is known in the art. Such radar systems transmit an electromagnetic wave toward the protected area (i.e., either omni-directionally or toward a selected sector) and detect and analyze reflections of the electromagnetic wave from objects in the protected area. The reflections of the electromagnetic wave are analyzed to determine at least the existence of objects and may further be determined, the position and additional properties of the objects. These properties may be, for example, the location of the object (e.g., relative to the radar system), the orientation of the object and the trajectory of the object or the velocity of the object (i.e., the speed and direction of motion of the object). Typically, State the art, radar systems scans the protected area by transmitting the electromagnetic wave via a mechanically rotating directional antenna. Alternatively, state of the art radar systems scan the protected area using an array of antennas (i.e., a transmitting array, a receiving array or both).
U.S. Pat. No. 6,573,857, to Fullerton et al, entitled “System and Method for Intrusion Detection using a Time Domain Radar Array” is directed toward using a sparse array of time modulated ultra wide band radars for intrusion detection. The system to Fullerton includes a plurality of Time Modulated (TM) Ultra-Wide Band (UWB) radars (abbreviated TM-UWB radars) positioned around the protected area. Each TM-UWB radar transmits a UWB pulse or pulses (i.e., a short pulse of low duty cycle) toward the protected area. Each TM-UWB radar receives reflections of these transmitted pulses from objects in the protected area. The range of an object from each TM-UWB radar is determined according to the time-of-flight of the pulse (i.e., from the TM-UWB radar to the object and back to the TM-UWB radar). The position of the object is determined according to the ranges of the object from each one of the TM-UWB radars. Thus, the system to Fullerton creates a radar image of the protected area.
With a stationary target, each signal received after an initial scan of the monitored area will appear substantially identical whereas physical movement within the monitored area will alter the characteristic of the received signals. The received signals are continuously averaged to generate a nominal received signal. The average received signal is subtracted from each succeeding received signal. As stated above, if there is no movement within the monitored area the average received signal and each succeeding received signal will be substantially identical and no signal will result following the subtraction process. If movement does occur within the monitored area, a signal will result after the subtraction process. With a stationary target is present, each signal received after an initial scan of the monitored area will appear substantially identical. Physical movement within the monitored area will alter the characteristic of the received signals. The received signals are continuously averaged to generate a nominal received signal. The average received signal is subtracted from each succeeding received signal to determine movement.